You can always do negatives. Put a bar around shoulder height, stand straight, grab it, and slowly lift your legs. You will start to slide down because you can’t hold your bodyweight without putting your legs on the ground. So you’ll slide down. Congratulations, you did a negative pull-up.
I mean you’re literally just standing normally, holding onto something, and then slowly putting weight on what you’re holding onto. I really can’t see how this can go wrong.
Only if you can’t stand or can’t move your arms or something would this not be possible.